Download
1 / 19
190 likes | 405 Views
EML 4230 Introduction to Composite Materials. Chapter 5 Design and Analysis of a Laminate The Drive Shaft Problem Dr . Autar Kaw Department of Mechanical Engineering University of South Florida, Tampa, FL 33620 Courtesy of the Textbook Mechanics of Composite Materials by Kaw.
E N D
EML 4230 Introduction to Composite Materials Chapter 5 Design and Analysis of a Laminate The Drive Shaft Problem Dr. Autar Kaw Department of Mechanical Engineering University of South Florida, Tampa, FL 33620 Courtesy of the Textbook Mechanics of Composite Materials by Kaw
A drive shaft for a Chevy Pickup truck is made of steel. Check whether replacing it with a drive shaft made of composite materials will save weight? Problem Statement
Why composite materials? • Light weight___ reduces energy consumption; increases amount of power transmitted to the wheels. About 17-22% of engine power is lost to rotating the mass of the drive train. • Fatigue resistant___ durable life. • Non-corrosive___ reduced maintenance cost and increased life. • Single piece___ reduces manufacturing cost.
Why composite materials? • Prevent injuries – the composite drive shaft “broom” on failure
Problem Description Design Constraints 1. Maximum horsepower= 175 HP @4200 rpm 2. Maximum torque = 265 lb-ft @2800 rpm 3. Factor of safety = 3 3. Outside radius = 1.75 in 4. Length = 43.5 in
Torque in Drive Shaft In first gear - the speed is 2800 rpm (46.67 rev/s) - assume ground speed of 23 mph (405 in/sec) Diameter of tire = 27 in Revolutions of tire =405/[π(27)] = 4.78 rev/s Differential ratio = 3.42 Drive shaft speed = 4.78 x 3.42 = 16.35 rev/s Torque in drive shaft = (265x46.7)/16.35 = 755 lb-ft
Maximum Frequency of Shaft Maximum Speed = 100 mph (1760 in/sec) Diameter of tire = 27 in Revolutions of tire =1760/[π(27)] = 20.74 rev/s Differential ratio = 3.42 Drive shaft speed = 20.74x3.42 = 71Hz
Design Parameters • Torque Resistance. • Should carry load without failure • Not rotate close to natural frequency. • Need high natural frequency otherwise whirling may take place • Buckling Resistance. • May buckle before failing
Steel Shaft – Torque Resistance Shear Strength, max = 25 Ksi Torque, T = 755 lb-ft Factor of Safety, FS = 3 Outer Radius, c = 1.75 in Polar moment of area, J = cin=1.69 in t = 1.75-1.69 = 0.06 in = 1/16 in
Steel Shaft - Natural Frequency fn = Acceleration due to gravity, g= 32.2 ft/s2 Young’s modulus, E = 30 Msi Weight per unit length, W = 0.19011 lbf/in Length, L = 43.5 in Second Moment of Area, I = fn= 204 Hz Meets minimum of 71.1Hz
Steel Shaft - Torsional Buckling T= Mean radius, rm = 1.6875 in Thickness, t = 1/16 in Young’s modulus, E = 30 Msi Critical Buckling Load, T = 5519 lb-ft Meets minimum of 755 lb-ft
Load calculations for PROMAL Nxy = (Why) T = 755 lb-ft r = 1.75 in Nxy= 470.8 lb / in Neglecting centrifugal force contribution
Composite Shaft-Torque Resistance Inputs to PROMAL: Glass/Epoxy from Table 2.1 Lamina Thickness = 0.0049213 in Stacking Sequence: (45/-45/45/-45/45)s Load Nxy = 470.8 lb / in Outputs of PROMAL: Smallest Strength Ratio = 1.52 (not safe) Thickness of Laminate: h = 0.0049213*10 = 0.04921 in
Composite Shaft - Natural Frequency fn = g = 32.2 ft/s2 Ex = 1.814 Msi I = 0.7942 in4 W = 0.03438 lbf/in L = 43.5 in Hence fn= 105.6 Hz (meets minimum 71.1 Hz)
Composite Shaft - Torsional Buckling T = rm = 1.75 -0.04921/2= 1.72539 in t = 0.04921 in Ex = 1.814 Msi Ey= 1.814 Msi T = 183 lb-ft (does not meet 755 lb-ft torque)
